AU655318B2

AU655318B2 - Methods for inhibiting metal corrosion in aqueous systems

Info

Publication number: AU655318B2
Application number: AU25360/92A
Authority: AU
Inventors: Gary Edwin Geiger; Roger Cletus May; William John Yorke
Original assignee: Betz International Inc
Current assignee: Suez WTS International USA Inc
Priority date: 1991-09-30
Filing date: 1992-09-25
Publication date: 1994-12-15
Anticipated expiration: 2012-09-25
Also published as: AU2536092A; CA2074983A1

Description

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655318

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANIDARD PATENT t'tt t I, I lilt I, It i I.

II. 4 I, I t ci Applicant BETZ INTERNATIONAL, INC.

A.R.B.N. 001 775 551 Invention Title: METHODS FOR INHIBITING METAL CORROSION IN AQUEOUS SYSTEMS The following statement is a full description of this invention, including the best method of performing it known to me/us:

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Y-713 METHODS FOR INHIBITING METAL CORROSION IN AQUEOUS SYSTEMS FIELD OF THE INVENTION The present invention pertains to methods for inhibiting the corrosion of metals in aqueous systems. The present invention 5 more particularly pertains to simultaneously inhibiting the corrosion of iron-containing and copper-containing metals in cooling water systems that are contaminated by sour leaks.

BACKGROUND OF THE INVENTION In many refining operations, cooling water systems are 10 often used. Heat exchangers and refrigeration units are commonly used during petrochemical and refining operations. Water is used as the heat exchange fluid.

Iron and/or copper-bearing alloys are commonly the metals of fabrication of heat exchangers, as well as othdf parts in contact with cooling water, such as pump impellers, stators, and valve parts. -2- The cooling water systems most often used are of the recirculating type so that the water is used repetitively and remains in contact with the metals of the cooling system. In refinery operations, these cooling waters are often contaminated by "sour" leaks which contain hydrocarbons, organic sulfides and hydrogen sulfide.

These contaminants can be very deleterious if they are left untreated. They will quickly overwhelm any standard operating treatment. The hydrocarbons can coat the metal surfaces of I 10 the cooling system and prevent corrosion inhibitors from working I correctly. Sulfide ions can cause severe corrosion of metals, I which can eventually result in catastrophic failure of metal i components.

Sour leaks and the attendant corrosion and scale problems 15 have been problematic in refineries for years, despite various attempts to inhibit their effects. When these leaks have overwhelmed standard treatments, remedial additive treatments were introduced which typically addressed a specific metallurgy, and at best offered limited improvement. The inventors of the present invention have surprisingly found that the methods described herein provide simultaneously effective inhibition for both iron-containing and copper-containing metals exposed to sour 3 leaks.

SUMMARY OF THE INVENTION I I (i I I, The present invention provides for methods for inhibiting the corrosion of metal in aqueous systems. Alkyl benzotriazole compounds such as butyl benzotriazole have been found to effectively inhibit the corrosion of iron-containing and copper-containing metals in contact with cooling water systems that contain sulfides and hydrocarbons as a result of a sour leak.

DESCRIPTION OF THE RELATED ART U.S. Patent No. 3,029,202, Brown et al., April 1962 10 describes methods of treating water containing sulfur impurities using oxidation catalysts.

U.S. Patent No. 4,680,127, Edmondson, July 1987 discloses a method for reducing the amount of hydrogen sulfide in an aqueous system. The methods provide for adding a combination of glyoxal 15 and formaldehyde or glutaraldehyde or glyoxal alone to the aqueous medium.

U.S. Patent No. 4,867,944, Bucher et al., September 1989 discloses a method for inhibiting the corrosion of carbon steel in cooling tower systems. The corrosion inhibiting composition comprises a water soluble zinc compound, a water-soluble molybdate compound, a water-soluble orthophosphate, a water-soluble polyphosphate and a dispersant.

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-4- Rogers, et al., National Association of Corrosion Engineers, Corrosion 87, Conference Paper No. 151 (1987), discloses treating sour leaks in heat exchanger systems. The methods employ triazoles such as benzotriazole in combination with sequestrants to inhibit corrosion in cooling systems. The use of azoles alone yielded inadequate inhibition.

Schreifels, et al., Corrosion, Vol. 45(1989), pp.

84-91, discloses experimental results for benzotriazole and 2-mercaptothiazole as copper corrosion inhibitors in kerosene.

These compounds did not inhibit copper sulfide formation.

Japanese Patent 51-139,162 discloses making an antifouling composition useful in suppressing pitting of a copper alloy by the action of a sulfide comprising treating a water insoluble compound with an n'qanic solvent, a surfactant and a 15 benzotriazole compound.

t British Patent No. 1,065,995 teaches that 5-alkyl substituted benzotriazoles are effective in reducing corrosion or S' tarnish of copper items in glycolic solvents or in lubricants, or to resist tarnishing in the presence of atmospheric sulfides.

t 1 20 United States No. 4,744,950, Hollander, May 1988 discloses a method of providing a corrosion inhibiting film on copper-containing metals in contact with an open cooling water system. The films, are provided by C 3 to C 6 substituted alkyl benzotriazoles.

i* DETAILED DESCRIPTION OF THE INVENTION Methods for inhibiting the corrosion of iron-containing and copper-containing metals in contact with cooling water are described. These methods comprise adding to said cooling water containing sulfides, hydrocarbons and mixtures thereof an effective amount for the purpose of an alkyl benzotriazole compound.

The methods of the present invention are particularly useful when the aqueous system is contaminated by a sour leak.

These aqueous systems are mostly cooling water systems associated with refinery operations. These leaks contain sulfides and hydrocarbons such as crude oil, diesel fuel, naphthas, kerosene and gasoline cut hydrocarbons. In a typical refinery operation, both sulfides and hydrocarbons will be present in a cooling system that is experiencing a sour leak. The introduction of these contaminants will rapidly cause corrosive attack of the ironsystem.

The methods of the present invention can be applied to cooling water systems that are not suffering from sour leaks but merely to treat for residual sulfide ions. These methods can also be applied with other corrosion inhibiting agents, as well as microbiological control species such as oxidizing and nonoxidizing biocides.

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-6- A particular advantage of the present invention is that it maintains low corrosion rates for both iron and copper metallurgies simultaneously under the extremely aggressive conditions that occur when both an oxidizing biocide, such as chlorine, and sulfide are present in the system at the same time. In fact, the addition of chlorine is often increased in response to sour leaks.

The preferred alkyl benzotriazole compound is butyl benzotriazole. Tt;e compounds may be applied in any conventional Smanner and can be fed to the cooling water neat or by any suitable carrier means. Water, glycol and polyglycols can be used as the solvent. However, aqueous solutions are preferred.

The addition of the compounds to the cooling water can be either intermittent or continuous, continuous being preferred.

The treatment dosages of the alkyl benzotriazole compounds are 15 dependent upon the severity of the sour leak. Accordingly, a ,range from about 0.1 parts per million to about 100 parts per million alkyl benzotriazole compound should be added. Preferably, ;the compound should be added from about 1 part per million to about 15 parts per million.

The data set forth below demonstrate the unexpected results occasioned by use of this invention. The following example is included as being an illustration of the invention and should not be construed as limiting the scope thereof.

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EXAMPLE

Chlorinated recirculator testing was performed using the treated water as described in Table A. The sour leak was simulated by the continual feed of the equivalent of 2 parts per million (as H 9 S) of aqueous sodium sulfide to the recirculator. The temperature was kept at 120 0 F and the pH was actively controlled at 7.2. The condition of chlorination was simulated by the continual feed of 0.9% solution of sodium hypochlorite at the rate of 1 ml per hour into the 11 liter system. Butyl benzotriazole was added to the treated water as an additional inhibitor at a level of 6 parts per million. Both low carbon steel and Admiralty brass ccoupons were exposed to the water for 7 days. The test results appear in Table I.

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-8- TABLE A Ca+2(ppm as CaC0 3 600 Mg+ 2 (ppm as CaCO 3 264 Cl (ppm as C1-) 555 SSO4- 2 (ppm as S04-2) 400 Silicate (ppm as Si02) Orthophosphate (ppm as P0 4 3 12 Pyrophosphate (ppm as P0 4 3 Tolyltriazole (ppm) 4

HEDP

1 (ppm) 1.6 Active Polymer (ppm) 12 1 HEDP l-hydroxyethylidene-1,1-diphosphonic acid TABLE I Steel Brass Corrosion Corrosion Additional Rate Rate S"Leak Condition Inhibitor (nmil/ r) (mil/vr) Sour leak nbne 7.4 2.6 Sour leak Butyl-BZT 1.4 0.7 I 20 Butyl-BZT Butyl Benzotriazole Table I indicates the ability to protect both steel and copper containing metals in the presence of sulfides and chlorination. The visual appearance of the coupons and the heated -9steel tube present in the experiments showed less corrosion when butyl benzotriazole was present. These results are totally unexpected considering the severity of the laboratory test conditions and actual field experience.

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,c While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications will be obvious to those skilled in the art. The appended claims generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.

Claims

1. A method of simultaneously inhibiting the corrosion of iron-containing and copper-containing metals in contact with an aqueous system containing a contaminant selected from the group consisting of sulfides, hydrocarbons and mixtures thereof comprising adding to said aqueous system an effective amount for the purpose of an alkyl benzotriazole compound.

2. The method as claimed in claim 1 wherein said alkyl benzotriazole compound is butyl benzotriazole.

3. The method as claimed in claim 1 wherein from about 0.1 o, parts per million to about 100 parts per million of said alkyl benzotriazole compound is added to said aqueous system.

4. The method as claimed in claim 3 wherein from about 1 part per million to about 15 parts per million of said alkyl benzotriazole compound is added to said aqueous system.

The method as claimed in claim 1 wherein said alkyl 'benzotriazole compound is added intermittently. i

6. The method as claimed in claim 1 wherein an oxidizing biocide, or a non-oxidizing biocide, or a combination thereof is added to raid aqueous system.

7. The method as claimed in claim 6 wherein said oxidizing biocide is chlorine.

8. The method as claimed in claim 1 wherein said aqueous system is a cooling water system. DATED THIS 25TH DAY OF SEPTEMBER 1992 BETZ INTERNATIONAL, INC. By its Patent Attorneys: GRIFFITH HACK CO. Fellows Institute cf Patent Attorneys of Australia ii i ABSTRACT Methods are provided for inhibiting the corrosion of metals in certain aqueous systems. The methods comprise adding an effective amount of an alkyl benzotriazole compound to the system for which corrosion inhibition is desired. tr'c r